Staphylococcus aureus (S. aureus) is the second most common pathogen causing healthcare associated infection (HAI) in neonates. S. aureus strains with resistance to common antibiotics, specifically methicillin- resistant S. aureus (MRSA), account for up to 35% of S. aureus infections in neonates and have an associated mortality of up to 25%. Despite aggressive measures to prevent S. aureus infections in neonates, the burden of S. aureus disease remains high in this population. We propose a new approach to assess the effectiveness of decolonization for prevention of S. aureus transmission in the NICU. Our preliminary data suggest that MRSA transmission may be driven by untreated neonates and decolonization may reduce MRSA transmission in the NICU. We propose to use probabilistic models to assess the impact of decolonization and colonization pressure on MRSA transmission, while accounting for other relevant factors in transmission, such as healthcare worker hand hygiene compliance and MRSA strain type. Our long term goal is to identify and test interventions that will reduce MRSA transmission and infections in neonates. The specific aims are to optimize methods for measuring the independent effect of decolonization on MRSA transmission in the NICU, and to determine the impact of decolonization on MRSA transmission in neonates in a multicenter retrospective cohort study. In Sub aim 1, we will identify a cohort of neonates admitted to the JHH NICU and assess the impact of colonization pressure and decolonization on MRSA transmission using probabilistic models. In Sub aim 2, using data obtained from two collaborating NICUs, we will test the exportability of the methods and the validity of the findings established in Sub aim 1. The findings of this proposal could inform futur prospective studies or change practice outright.